In many art areas it is desirable to be able to remove dense impurities, such as sand, from fluids. Particularly in the art of pulp and paper manufacture, it is desirable to remove sand and like particles from liquids used in the manufacture of cellulosic pulp, such as digesting, washing and bleaching liquors. Conventionally this is accomplished utilizing a hydrocyclone, such as shown in U.S. Pat. No. 2,377,524. In such devices. the liquor is introduced into a tank with a forceful whirling motion. Heavier particles, such as sand, are driven by the centrifugal force of the whirling action toward the wall of the tank. When reaching the tank wall under the action of gravity such dense particles descend toward the bottom of the tank and exit an outlet in the tank bottom.
While prior art hydrocyclones are generally successful in performing the desired separation of dense impurities from liquid, there are some problems associated therewith. Since the lower portion of the hydrocyclone is conventionally conical, the fluid vortex is constricted adjacent the tank bottom so that the fluid has a gradually increasing angular velocity. At a certain vertical zone of the tank wall, the resultant of the forces acting upon the sand particles--centrifugal force and the force of gravity--will be directed perpendicularly to the tank wall. This results in vertical stagnation of the dense particles at the wall in that zone, instead of the particles moving downwardly toward the bottom outlet. While vertically stagnated, the particles travel in a circular motion under the influence of the fluid's centrifugal force, causing abrasion between the particles and the tank side wall. The result of this abrasion is a weakening of the tank side wall, and--depending upon the abrasiveness of the particles--puncture of the tank wall after a relatively short operating time.
Prior attempts to overcome the problem of tank side wall damage as a result of particle stagnation have included the insertion of vertical plates in the stagnation area, and the design of the conicity of the tank lower section so that there is a relatively gradual taper of the conical section. Each of these techniques, however, results in a dampening of the whirling motion of the fluid, and thus impairs the ability of the hydrocyclone to effect dense particle separation.
According to the apparatus and method of the present invention, it is possible to prevent vertical stagnation of dense impurities against the side wall interior of a hydrocyclone without dampening the whirling motion imparted to the fluid. The result is a much longer life of the tank side wall for a given abrasiveness of the particles to be separated. Additionally, the portion of the apparatus at which stagnation is likely to occur is replaceable so that the entire hydrocyclone tank need not be replaced or repaired if damage should still occur as a result of vertical stagnation of particles.
According to one aspect of the apparatus of the present invention, a vertically upstanding tank substantially circular in cross-section is provided, which tank includes a top wall, bottom wall, and side wall. Means are provided for introducing, tangentially to the side wall, fluid having dense impurities into the tank adjacent the top wall thereof to impart whirling motion to the fluid within the tank. A fluid outlet is disposed substantially centrally in the top wall of the tank and an impurities outlet is disposed centrally in the bottom wall of the tank. Means are provided for preventing vertical stagnation of dense impurities against the side wall interior at a particular vertical level without dampening the whirling motion imparted to the fluid. Such means comprise a funnel means; means defining perforations (larger than the average dimensions of the impurities) in the funnel means at areas thereof wherein stagnation of dense impurities is likely to occur; and means for operatively mounting the funnel means to the tank side wall between the suspension inlet and the impurities outlet so that dense impurities being separated must pass through the funnel means in transit to the impurities outlet, and so that the funnel means at the perforated areas thereof is spaced from the tank side wall and the impurities outlet is in open communication with the interior of the funnel means through the perforations.
Preferably the funnel means according to the invention comprises a conical member having an open large end mounted above a small end thereof, and the means for mounting the funnel means to the tank's side walls comprises an annular flange rigidly mounted to the exterior of the funnel means, and clamping means associated with upper and lower sections of the side wall for receiving the flange therebetween and holding it in place with respect to the side wall. The tank side wall upper section may include a top cylindrical portion and a bottom conical portion having a clamping means associated therewith, and the conical member and the tank upper section conical bottom portion have substantially the same conicity--preferably about 15.degree. to 30.degree.. Alternatively, the tank side wall may comprise a cylindrical upper portion and a conical lower portion with the means for mounting the funnel means to the tank side wall comprising means for rigidly attaching the funnel large end to the interior of the side wall at the cylindrical portion so that the funnel means extends concentrically downwardly into the tank lower portion spaced from the side wall lower portion. In order to facilitate discharge of separated impurities through the impurities outlet, means may be provided for introducing liquid under pressure tangentially into the volume between the funnel and the tank bottom wall, the liquid being introduced in this area being introduced with a much calmer whirling action than the whirling action imparted to the fluid at the fluid inlet.
According to another aspect of the present invention, apparatus is provided for removing dense particles from a suspension comprising a vertically upstanding tank substantially circular in cross-section including a top wall, bottom wall, and side wall. A first conduit is provided in communication with the tank interior and extending tangentially to the side wall, and adjacent the top wall. A second conduit is disposed substantially centrally in the top wall of the tank and a third conduit is disposed substantially centrally in the bottom wall of the tank. Funnel means having a relatively large open end and a relatively small second end are provided with means defining perforations larger than the average dimension of the dense particles in at least areas of the funnel means adjacent the second end thereof, and means are provided for operatively mounting the funnel means to the tank side wall. The mounting means mount the funnel between the first conduit and the third conduit so that the funnel means first end is vertically above the second end, so that any suspension, particles, or the like passing between the first and third conduits must pass through the funnel means, and so that the funnel means at the perforated areas thereof is spaced from the tank side wall with the funnel means second end above the third conduit and with the third conduit being in open communication with the interior of the funnel means through the perforations.
According to the method of the present invention, separation of sand or like dense impurities from the fluid containing the impurities is provided. The method comprises (or consists of) the following steps: (a) Introducing fluid containing sand or like dense impurities into the first conduit of the apparatus to impart a whirling motion to the fluid within the tank. (b) Removing fluid with the sand or like dense impurities separated therefrom through the second conduit of the apparatus. (c) Removing sand or like dense impurities separated from the liquid through the third conduit of the apparatus; and (d) preventing vertical stagnation of dense impurities against the side wall interior at a particular vertical level without dampening the whirling motion imparted to the fluid. Step (d) is accomplished by utilizing a funnel having an open large first end and a small second end with perforations disposed in at least the area of the funnel adjacent the second end, and by operatively mounting the funnel to the tank side walls so that the first end thereof is vertically above the second end, and so that all sand or like dense impurities to pass through the third conduit must pass through the funnel, and so that the funnel at the areas thereof containing the perforations is spaced from the tank side wall is in open communication with the third conduit. Step (c) may be accomplished in part by introducing liquid under pressure tangentially to the tank side wall into the tank interior between the funnel and the third conduit to provide a whirling action which entrains separated sand or like dense impurities and carries it through the third conduit. The whirling action of the liquid in accomplishing step (c) is calmer than the whirling action of fluid in accomplishing step (a).
It is the primary object of the present invention to prevent vertical stagnation of dense impurities against the side wall interior of a hydrocyclone or the like without dampening the whirling motion imparted to the fluid. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.